The detection technique for an ion migration spectrum was firstly proposed by Karasek and Cohen as a method for analyzing organic compounds in 1970. From the beginning, the IMS has already aroused people's strong interest, however, until the end of the 1980s, did people begin to grasp some difficulties in the IMS such as the process of molecular chemical ionization under the atmospheric pressure (APCI), thereby greatly improving the performance of the IMS which is then broadly applied to various aspects. At present, the products based on IMS have been widely used for detecting exploders, drugs, chemical reagents at the airport, dock, station, etc. The IMS has become one of the existing broadly-used technologies for detecting trace chemicals due to its advantages of high sensitivity (10-8 to 10-14 g), short analysis time, strong function, and not too high cost, etc.
FIGS. 1 and 2 illustrate a structural diagram of a conventional IMS system and its front end (namely a migration tube) respectively. As illustrated in FIG. 1, the conventional IMS system is comprised of a sampling system 101 for sampling; a carrier gas preparation system 102 and a carrier gas exhausting system 103 for preparing carrier gas and exhausting carrier gas, respectively; a migration gas preparation system 104 and a migration gas exhausting system 105 for preparing migration gas and exhausting migration gas respectively; a migration tube 106 as the core part of the IMS system; an ion gate of the migration tube 106 and a controller 107; a high-pressure generator and controller 108 and a temperature sensor and controller 109; and a migration spectrum detector 110. The migration spectrum detector 110 comprises a micro-current amplifier 1101 for amplifying the current detected by a charge sensor 206 in the migration tube 106, an A/D converter 1102 for digitizing the amplified current value; and a migration spectrum acquirement device 1103 for performing calibration on the digitized current signals to acquire an eventual migration spectrum.
As illustrated in FIG. 2, the migration tube 106 mainly comprises a gasifier 201, an ion source 202, a reaction region 203, an ion gate 204, a drift region 205, a charge sensor 206, a sample inlet 211, a carrier gas inlet 212 and outlet 213, a migration gas inlet 214 and outlet 215. The basic operation principles of the IMS are described as follows:
1. A sample (solid sample or gas sample) containing suspect substances enters into the migration tube 106 via the sampling system 101.
2. After the sample has been gasified by gasifier 201, molecules of the suspect substances enter into the ion source 202 and are ionized into molecular ions.
3. The mixed ions are introduced into the reaction region 203 via an electrical field where the molecular ions have been fully reacted with each other.
4. The ion gate 204 is initiated to cause the ions to drift in the drift region 205 with a constant electric field intensity which is filled with gas.
5. The charge sensor 206 senses time for the ions to pass through the drift region.
6. The time for different ions to pass through the drift region 205 to the charge sensor 206 is different due to the different characteristics of the ions, thus, the arrival time of the charges detected by the charge sensor 206 is related to the characteristics of the ions, so the migration spectrum detector 110 can acquire a one-dimensional time ion migration spectrum related to the characteristics of the ions by processing the detection results of the charge sensor 206.
7. Various processing are performed on the ion migration spectrum and a characteristic ion peak of the suspect substance is identified from the ion migration spectrum via a software algorithm, so that an appropriate alarm information can be generated accordingly.
Since the ion migration spectrum is easily interfered by the peaks of various interference substance, the pressure and temperature of the atmosphere, and the ion migration spectrum is complicated by the mechanical vibration, electronics noise and so on. So, the key for improving detection sensitivity and accuracy of the suspect substances by the ion migration spectrometer and reducing the false alarm rate is to find the characteristic ion migration peak of the suspect substance accurately and efficiently and to eliminate various interferences as much as possible. Currently, there are various methods for processing and seeking a ion migration peak. However, there is no good way to eliminate various interferences and find the characteristic ion migration peak of the suspect substance accurately and efficiently.
Thus, what is desired is an improved method for performing spectrum process and peak search on the ion migration spectrum, eliminating various interferences, seeking a characteristic ion migration peak of the suspect substance accurately and efficiently, improving detection sensitivity and accuracy of the suspect substance by the ion migration spectrometer and reducing the false alarm rate, as well as an ion migration spectrometer using the method.